All motors generate heat. In the case of a submersible motor, heat is dissipated to the cooling flow of water drawn past the motor by the pump driven by the motor. If the cooling flow is interrupted, the motor can overheat and fail.
It is known to connect a power line communications (PLC) transmitter to the wye or neutral point of the motor to transmit a modulated signal through the motor and the power lines and to couple a receiver to the power lines to demodulate the modulated signal and extract relevant information. These neutral point systems require significant processing capacity to modulate the information over the power lines. Furthermore, connection to the neutral point limits where the transmitter can be placed to minimize cost or, alternatively, increases manufacturing complexity and cost if the transmitter is placed remotely from the neutral point. The high costs associated with modulation through the wye or neutral point may be justified where the power lines exhibit a high amount of noise due to, for example, use of a variable speed drive to provide a variable frequency voltage to the motor. The variable frequency voltage is typically generated by switching a DC voltage, with a power module comprising power switches, at frequencies between 2 KHz and 10 KHz. The switching frequencies generate noise, therefore complex systems are needed to communicate information from the motor to the surface.
Some applications do not justify the high cost of modulation through a neutral point system to overcome noise. Therefore, a need exists for a relatively low cost power line communication system.